In a camera, a typical passive automatic focusing method can be used by evaluating contrast values within a consecutive range near a focus point of a subject located at a center area of a scene. An automatic focusing operation is performed by precisely moving the lens group of the camera within the consecutive range to determine the focus point where the subject has a maximum contrast. During the automatic focusing operation, a number of brightness values of the environment of the subject are also determined.
However, when a digital camera takes pictures of the subject in an environment lit by discharge lamps (e.g., fluorescent lamps which operate directly from AC power supplies), there is a possibility for the digital camera to detect a low brightness value of the environment during the automatic focusing operation due to flickering of the fluorescent lamp at a certain frequency. As a result, the maximum contrast value of the subject may not be reliable found during the automatic focusing operation. Accordingly, the automatic focusing operation is affected.